Traditional cigarettes are smoked by lighting an end of a wrapped tobacco rod and drawing air predominately through the lit end by suction at a mouthpiece end of the cigarette. Traditional cigarettes deliver smoke as a result of combustion, during which tobacco is combusted at temperatures that typically exceed 800° C. during a puff. The heat of combustion releases various gaseous combustion products and distillates from the tobacco. As these gaseous products are drawn through the cigarette, they cool and condense to form an aerosol, which provides the flavors and aromas associated with smoking.
An alternative to the more traditional cigarette is an electrically heated cigarette used in electrical smoking systems. As compared to traditional cigarettes, electrical smoking systems significantly reduce sidestream smoke, and also permit smokers to suspend and reinitiate smoking as desired. Exemplary electrical smoking systems are disclosed in commonly-owned U.S. Pat. Nos. 6,026,820; 5,988,176; 5,915,387; 5,692,526; 5,692,525; 5,666,976; 5,499,636; and 5,388,594, each of which is hereby incorporated by reference in its entirety.
Electrical smoking systems include an electrically powered lighter and an electrically heated cigarette, which is constructed to cooperate with the lighter. It is desirable that electrical smoking systems be capable of delivering smoke in a manner similar to the smoker's experiences with traditional cigarettes, such as by providing an immediacy response (smoke delivery occurring immediately upon draw), a desired level of delivery (that correlates with FTC tar level), a desired resistance to draw (RTD), as well as puff-to-puff and cigarette-to-cigarette consistency.
Volatile flavorings have been incorporated in traditional cigarettes to add flavors and aromas to mainstream and sidestream tobacco smoke. See, for example, U.S. Pat. Nos. 3,006,347; 3,236,244; 3,344,796; 3,426,011; 3,972,335; 4,715,390; 5,137,034; 5,144,964; and 6,325,859, and commonly-owned International Publication No. WO 01/80671. The added flavorings are desirably volatilized when the cigarette is smoked. However, volatile flavorings tend to migrate in the cigarette to other components and possibly through the entire cigarette.
Volatile flavorings can be lost from cigarettes during storage and distribution at ordinary conditions prior to smoking of the cigarettes. The degree of migration of volatile flavorings in cigarettes depends on different factors, including the flavoring's vapor pressure, the solubility of the flavoring in other components of the cigarette, and temperature and humidity conditions.
Flavorings also can chemically and/or physically deteriorate by contacting and/or reacting with other components of the cigarette, as well as with the environment. For example, activated carbon has been incorporated in cigarettes to remove gas-phase constituents from mainstream smoke. However, flavorings that have been incorporated in the cigarettes along with the activated carbon can be adsorbed by the activated carbon, which can clog pores of the activated carbon and consequently deactivate the activated carbon, thereby diminishing its ability to filter tobacco smoke.
For the foregoing reasons, flavorings that have been incorporated in cigarettes have not been totally satisfactorily delivered to the smoker. Due to the flavoring loss, the uniformity of flavored cigarettes has not been totally satisfactory. In addition, the sorption of flavorings by sorbents in the cigarettes can deactivate the sorbents and thereby reduce the sorbent's ability to remove gas phase constituents from tobacco smoke.